Many dismutation and transalkylation catalysts whose main constituent is mordenite have already been described in the prior art. The type of mordenite used generally is a so-called "wide pores" mordenite i.e. a mordenite whose pores have a diameter of about 7 Angstroms, said diameter being of about 8 to 10 Angstroms in the catalyst ready for use, as disclosed in the U.S. Pat. No. 3,506,731 where mordenite is used in hydrogen form or in the two French patent applications No. 2 329 619 and 2 367 533 to the applicant.
Also U.S. Pat. No. 3,281,483 mentions mordenites essentially exchanged with silver or nickel ions; U.S. Pat. No. 3,780,121 mentions a mordenite exchanged with metal ions from group I.sub.B of the periodic classification of elements (copper, silver) which is characterized by a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio from 12 to 80; U.S. Pat. No. 3,629,351 also concerns a modernite containing metal ions from groups I.sub.B, V.sub.A, VI.sub.A, II.sub.A and VIII of the periodic classification of elements, and, finally, U.S. Pat. No. 3,476,821 discloses the use of a mordenite containing a sulfurized metal from group VIII and having preferably a SiO.sub.2 /Al.sub.2 /O.sub.3 molar ratio higher than 20.
According to the invention, the zeolite used as basic material for preparing the catalyst is a sodium-containing mordenite pertaining to the category of the so-called "wide pores" mordenites, i.e. mordenites whose main pores have a diameter from about 7 to 10 Angstroms, or "small pores" mordenites, i.e. mordenites whose main pores have a diameter of about 4 to 6 Angstroms, in sodic form. The mordenite used for manufacturing the catalysts described in the examples is in powder form or extruded in sodic form, sold under the trade name of zeolon by U.S. NORTON Company. It has an orthorhombic structure, a specific surface of about 400 to 500 m.sup.2.g.sup.-1, an adsorption capacity up to 13.5% by weight of water and a pore average diameter of about 7 Angstroms. As a result of this pore opening, said mordenite can absorb in its structure microporosity, in two hours at 28.degree. C. under 3333.05 Pa (25 mm Hg), from about 8 to 9% by weight of simple aromatic hydrocarbons such as benzene or toluene whose steric bulk is 6.8 Angstroms, from about 7 to 8% by weight of orthoxylene (in two hours, at 28.degree. C., under 933.26 Pa (7 mm Hg) or about 6 to 7% by weight of 2,2,4-trimethylpentane (isooctane) under 4933 Pa (37 mm Hg) at 28.degree. C.